An antenna installed in a mobile radio apparatus may produce degraded performance due to electrical interaction between a user's hand and the antenna in a state when a user holds it by the user's hand for use. Particularly, in an antenna installed outside the mobile radio apparatus, such as a helical antenna, the antenna performance is further deteriorated due to the significant electrical interaction when the user's hand is disposed near the antenna or a feed part in a state when the user holds it by the user's hand for use.
This is because, if the user's hand is disposed near the antenna or the feed part, the resonant frequency as well as the antenna impedance may vary, so that a mismatching loss increases in a measurement frequency. How to reduce such electrical interaction is a design issue of an antenna in a mobile radio apparatus industry.
Further to the aforementioned problem, as shown in the Patent Document 1, a method of improving the mismatching loss by optimizing the matching condition of the antenna disposed outside the mobile radio apparatus when a user's hand is disposed near the antenna has been conceived.
As an another example, a method of using a metal portion of upper and lower casings in a folder type mobile radio apparatus as an antenna has been proposed.
This folder type mobile radio apparatus includes, as shown in FIG. 14, upper and lower casings 1301 and 1302 connected with each other by a hinge portion 1303. The upper and lower cases 1301 and 1302 are pivoted on the hinge portion 1303 to change between the folded and unfolded states. In addition, the upper and low cases 1301 and 1302 are made of a plastic material which is an insulating resin.
A metal frame 1305 is provided on a plane where a display element 1304 of the upper case 1301 is disposed. Typically, the metal frame 1305 is made of a kind of metal such as magnesium alloy having high conductivity, light weight, and high mechanical strength. This allows the upper case 1301 having a thin plate shape to function as an antenna element as well as obtain necessary mechanical strength. The longer side of the metal frame has a length L1 of, for example, about 90 mm.
The metal frame 1305 and the metal hinge 1306 are attached to the upper case 1301 by a mounting screw 1307, so that the metal frame 1305 and the metal hinge 1306 are electrically connected, and the upper case 1301 and the metal hinge 1306 are mechanically fixed.
The metal hinge 1306 and the metal hinge 1308 are pivotably connected around a pivot axis 1309 also functioning as a connecting means. The metal hinges 1306 and 1308, and the pivot 1309 are made of conductive metal, and electrically connected with one another at respective contact points. The metal hinges 1306 and 1308, and the pivot 1309 constitute a hinge portion 1303.
A part of the metal hinge 1308 and the feed terminal 1310 are attached to the lower case 1302 by a mounting screw 1311, so that the metal hinge 1308 and the feed terminal 1310 are electrically connected, and the lower case 1302 and the metal hinge 1308 are mechanically fixed.
The feed terminal 1310 is connected to the wireless circuit 1314 through a matching circuit 1313 on a circuit board 1312 installed in the lower case 1302. The circuit board 1312 is a printed board on which circuit elements for implementing various functions of the mobile radio apparatus are mounted, and has a ground pattern formed on its almost entire surface to serve as a ground voltage of the circuit.
The folder type mobile radio apparatus having the aforementioned antenna provides improved antenna performance in comparison with the helical antenna mounted on an external portion and allows the electrical interaction with a user's hand to be reduced. Therefore, it is possible to obtain excellent antenna performance even in a state when a user holds the mobile radio apparatus by the user's hand for use.
Patent Document 1: JP-A-2003-158468.